Aircraft fuel and propeller pitch control



Jan. 26, 1954 c. F. WOOD ETAL AIRCRAFT FUEL AND PROPELLER PITCH CONTROL 7 Sheets-Sheet 1 Filed Feb. 24, 1949 NM ng SE M m. a w J & mm

INVENTORS Cyrus F. Wood Carl L. Sudler BY a,, fb,@w,.'.

ATTORN EY Jan. 26, 1954 c F. WOOD EIAL 2,667,228

AIRCRAFT FUEL AND PROPELLER PITCH CONTROL Filed Feb. 24, 1949 7 Sheets-Sheet z k V) b /500 REM 33 FIG. 3

flux line: H

I 310177 power lines I 757? WITNESSES: INVENTORS G F. W d uw/W aw: BY 0 5 QJSM ATTORNEY Jan. 26, 1954 c. F. WOOD ETAL 2,667,223

AIRCRAFT FUEL AND PROPELLER PITCH CONTROL Filed Feb. 24, 1949 7 Sheds-Sheet 3 4.0. Curi 1 5%" BY I ATTORN EY Jan. 26, 1954 c. F. wooo ETAL 2,667,228

AIRCRAFT FUEL AND PROPELLER PITCH CONTROL Filed Feb. 24, 1949 -7 Sheets-Sheet 4 cyrul Ful z FIG. 4b.

BY AT'II'OR'NEY Jan. 26, 1954 c. F. WOOD ETAL AIRCRAFT FUEL AND PROPELLER PITCH CONTROL Filed Feb. 24, 1949 7 Sheets-Sheet 5 INVENTORS Cyrus F. Wood 'Gcrl L. Sadler Jan. 26, 1954 c. F. WOOD ET AL AIRCRAFT FUEL AND PROPELLER PITCH CONTROL Filed Feb. 24, 1949 7 Sheets-Sheet 6 3& E

Jan. 26, 1954 c. F. wooo ETAL AIRCRAFT FUEL AND PROPELLER PITCH-CONTROL Filed Feb. 24, 1949 7 Sheets-She'et- 7 INVENTORS Cyrus F. Wood Cad L. Sadler FlG. 8.

BY 62,, W7 ATTORNEY Patentecl Jan. 26 1954 AIRCRAFT FUEL AND PROPELLER PITCH CONTROL Cyrus F. Wood, Swarthmore, Pa., and Carl L.

Sadler, Jr., Rockford assignments, to the 3 Claims.

The invention relates to propulsion plants, more particularly for aircraft, wherein a variable pitch propeller is driven by a turbine which drives a compressor furnishing air to support combustion of fluid fuel and to admix with the products of combustion to form a gaseous motive fluid for driving the turbine, and it has for an object to control operation thereof by varying the input of fuel and the propeller pitch by means of a system which is adjustable manually and which is responsive to torque of the driving connection between the turbine and the propeller to control the power delivered by the turbine to the propeller.

A further object of the invention is to provide fuel control and pitch control motors controlled by means of an electrical network receiving electrical inputs dependent upon operating characteristics, such as torque, temperature and speed, the arrangement being such that changes in the operating characteristics unbalance the network for operation of the motors to change the fuel input and propeller pitch until the network is rebalanced.

Another object of the invention is to provide fuel and pitch control servo-motors controlled by electronic means responsive to an electrical network receiving torque, temperature and speed inputs and having torque, temperature and speed settings.

A further object of the invention is to provide a gas turbine driving a variable pitch propeller through gearing together with means responsive to torque of the driving connection between the turbine and the propeller to control the flow of fuel to the turbine and the propeller pitch to avoid overloading the gearing.

A further object of the invention is to provide a controlling system of the above character, wherein in addition to torque, control is also effected in response to speed.

Another and more particular object of the invention is to provide an apparatus of the above character controlled in response to torque of the driving connection between the turbine and the propeller, in response to turbine speed, and in response to turbine temperature.

Variable pitch propellers are used with aircraft to provide for variation in engine power and flight speed without substantial change in engine speed by varying the fuel input and propeller pitch. In the ordinary arrangement, a governor controls the propeller pitch in response to a small range of speed change and the input of fuel is controlled manually. Thus, change in fuel input Ill., assignors, by mesne United States of America as represented by the Secretary of the Navy Application February 24, 1949, Serial No. 78,162

is accompanied by change in propeller pitch to change the propeller thrust for operation of the engine over its power range at its most economical speed.

To provide for proper operation of an aircraft propulsion plant wherein a gas turbine drives a variable and reversible pitch propeller, the control should be fast and accurate. While, as above suggested, the propeller pitch could be controlled in response to engine speed and while the flow of fuel could be controlled in response to turbine temperature and torque, such an arrangement would not be satisfactory for proper operation during starting or when operating with reversed propeller pitch. Although, these difficulties are met by having the propeller pitch controlled in response to temperature or torque or both temperature and torque and by having the fuel flow controlled in response to engine speed, such a system would not be sufficiently stable; and, to provide for stability, in accordance with the present invention, the torquemeter is connected to control both the fuel flow and propeller pitch. As torque acts ahead of temperature, it serves to stabilize both the temperature control and the speed control.

The control of a gas turbine plant driving a propeller is not only complicated by temperature, speed and compressor limitations, but, as rotating elements of the plant are connected together positively, it is important to provide a control arrangement taking into account these limitations and which shall achieve its purpose with stability. To provide for stability, the improved control arrangement quickly senses any change in power by being responsive to torque. If control of fuel flow were entirely in response to speed, then the inherent time delay would be such that, with other factors of control and all rotating parts of the plant mechanically connected together, poor stability would be a serious difficulty. As the power may be increased with change in either or both speed and tempera ture, it will be apparent that the same power may be developed at several different combinations of these factors, and it is desirable to provide for power development at the rotational speed and temperature giving an optimum fuel rate; however, in increasing the fuel rate to increase power and rotative speed, an increase in fuel rate in relation to rotative speed large enough to stall or choke the compressor should be avoided. Hence, in addition to the control of the input of fuel in response to torque, speed and temperature, these factors are used to control the proapparent that, for

speed may vary relatively, the torque increas- H vide, for a variable and reversible i wherein the ing means is operative to isolate the pitch control motor from control in response to torque,

peller pitch to assure of a good relation of fuel rate, speed and temperature providing good performance without stalling the compressor.

Witha gas turbine plant driving an aircraft propeller, not only must the temperature be kept within safe limits for the structural materials used, but power should be delivered to the propeller with the turbine operating at such speed and temperature that the compressor stall limit is not exceeded. Therefore, in accordance with the present invention, fuel control andpitch control motors are energized by means of a system subject to torque, speed and temperature control and provided with manually-operated torque, speed and temperature settings. trol is primarily in response to torque, with the speed and temperature outputs exerting supplementary or corrective efiects or the controlling outputs being added algebraically, so that power will be delivered to quired for the torque and without the temperature xceeding the stall limit. In this connection, as the propeller pitch is variable, it will be the same power, torque and ing as the speed decreases and vice versa; and, as control of temperature depends upon speed, it will be apparent that the regulating system may be'adjusted to vary the power delivered by the turbine to the propeller, the torque, speed and temperature controls working to secure a steady state condition of the system for each change in power and with the temperature control also operating to limit the fuel input in relation to turbine speed to give over-temperature protection. 'Furthermore, as fuel flow response to speed, provision is readily made for propeller pitch reversal. Aside from this interrelation of torque, temperature and speed controls, each is provided with settings and all of the settings are controlled by manual means operative from the cockpit. Accordingly, a further object is to provide apparatus of this character having these advantageous features,

Another object of the invention is to provide apparatus of the above character wherein fuel :flow is controlled in response to torque to promote stability.

A further object of the invention is to provide apparatus of the character aforesaid wherein the fuel flow is controlled by turbine speed to aid in starting and reversing the propeller.

- A further object of the invention is to 7 propitch propeller, a main controlling system of the above character manually-operable setting or adjustspeed and temperature and to subject it to manual control for'operation over the reverse pitch range.

A further object of the invention is to provide a controlling system of the character just described for a variable and reversible pitch propeller with means responsive to flight velocity to prevent reversal of pitch and adjustment of the propeller over the reverse pitch range if the flight velocity exceeds a predetermined amount.

A further object of the invention is to provide a plant of the above character wherein the amount or" the change in the flow of fuel and pitch of the propeller, in response to changes in temperature, rotational speed, or torque of the driving connection between the turbine and the Con.-

he propeller at the speed reis controlled in strain gauge type Serves the present purpose very satisfactorily andhas anelectrical output, and an electric tachometer may be used and which provides an electrical output. The regulating system embodies a network supplied with torque, temperature and speed electrical inputs to develop an output controlling the flow of fue1 for operation of the turbine and controlling the propeller pitch to control the power delivered from the turbine to the propeller. The torque and speed inputs control the torque and speed for the power delivered by the turbine to the propeller and the temperature input provides for control at a favorable fuel rate with maintenance of a speed and temperature relation so as toavoid stalling of the compressor. Such an arrange ment readily provides for raising and lowering of torque, temperature and speed in proper rention, control in response to altitude and flight velocity, avoidance of reversing the propeller pitch if the fiight'velocity exceeds a predetermined amount, relative adjustment for stability and proper operating relation, and ready changeover from the main control system to the emergency control system in response to emergency operating conditions; Accordingly, a more particular object of the invention is to provide a Another object of the invention is to compensate the speed control in apparatus of th above character to minimize deviation of turbine speed from the set value.

A further object of the invention is to provide servo-motor mechanism for controlling the flow of fuel and the propeller pitch and controlled by vacuum tubes which are controlled in response to ttorque, speed and temperature electrical outpu s.

A further object of the invention is to provide a main system subject to torque, speed and'temperature control and which is manually adjustable to vary the power delivered by the turbine to the propeller together with an emergency system which is normally ineffective but which is automatically rendered effective in response to an emergency operating condition, the emergency system comprising speed control of pitch and fuel-air ratio control of the fuel input.

Another object of the invention is to provide means movable manually to adjust the torque, speed and temperature settings of apparatus'of the character aforesaid wherein the manual means is movable through a first range to adjust the speed setting to bring the turbine speed up to a desired value and then is movable through fuel input to rotative speed;

a second range to adjust the torque, speed and temperature settings to increase the power delivered by the turbine to the propeller.

Another object of the invention is to provide manually-movable means for adjusting the torque, speed and temperature settings of the aforesaid apparatus such that movement through a first range is effective to bring the turbine to full speed, movement through a second range is effective to increase the power delivered to the propeller by the turbine with the latter operating at full speed, and movable through a third range, with the turbine operating at full speed, to reverse the propeller pitch and control the pitch over the reverse pitch range provided that the flight velocity does not exceed a predetermined amount.

The foregoing and other objects are effected by our invention as will be apparent from the following description and claims taken in connection with the accompanying drawings, forming a part of this application, in which:

Fig. 1 is an elevational view showing a reversible and variable pitch propeller driven by a gas turbine plant with .the improved controlling arrangement applied thereto;

Fig. 2 is a diagram showing the relationship of Fig. 3 is a diagram showing temperature curves as related to thrust or power and engine speed;

Figs. 4A, 4B and 4C collectively constitute a diagrammatic view showing electrical controlling apparatus;

Fig. 5 is a simplified diagrammatic view showing essential components and relations of Figs. 4A, 4B and 40;

Fig. 6 is a fragmentary view of an electric torquemeter;

Figs. 7 and 8 are graphs indicating operating conditions in relation to engine speed and condition lever and power lever positions;

Figs. 9 and 10 show the interlock arrangement for the condition and. power levers; and

Fig. 11 is a detail view showing diagrammatically a variable pitch propeller and its operating means together with electrical means effective to shift control of the propeller pitch from the main to the emergency system.

:In the drawings, there is shown a gas turbine plant, at I 0, having a power shaft I l transmitting power, through two-stage reduction gearing l2, to a propeller M. The gas turbine plant comprises a gas turbine l5 driving a compressor I6 furnishing air to combustor means I8 to support combustion of liquid fuel supplied thereto and to admix with the products of combustion to form gaseous motive fluid for operation of the turbine.

The present invention is concerned with a main control system subject to manual control from the cockpit and which is responsive to torque, temperature and speed to vary the propeller pitch and the input of fuel to the combustor automatically in accordance therewith and it is also concerned with an emergency system for controlling the propeller in response to speed with manual control of the fuel input in the event of a plant operating condition including failure of the main control.

The principal feature of the invention is the main control system including torque, temperature and speed regulators operative to control the propeller pitch and to vary the fuel input in response to torque, speed and temperature for operation of the plant over the power and speed 'range stably and with good performance and 6 wherein over-temperatures bring about fuel restriction to limit the temperature and. thereby avoid stalling of the compressor.

A second feature of the invention is an emer- The main control system includes torque and temperature regulators which operate to oppose change in torque and temperature and which have settings operative-to increase and decrease the torque and temperature levels. Increase in either torque or temperature brings about a response which results in reduction in fuel input and propeller pitch. -The main control system also includes a speed regulatorhaving a setting; however, an increase in speed results'in reductioniin fuel input and increase in propeller pitch. .As control offue1 input and propeller pitch is pri marily in response to torque, operating conditions are'rapidly sensed and the lag or inertia effects involved with speed andtemperature responses are minimized, whereby operation with stability is promoted. While the control system is isochrcnous and temperature control is linked to speed control, torque control is efiective to anticipate temperature and speed changes where the latter are due to changes in fuel flow... Furthermore, torque control stabilizes the system as changes in torque are opposed by changes in temperature. Also, the main control system uniquely and inherently provides for operation at high thermal efficiency without stalling the compressor, as will now be immediately pointed out.

The advantage of control of fuel input and propeller pitch primarily in response to torque will be clearer from a consideration of performance diagrams, Figs. 2 and 3, which show that the engine may be started and brought up to ground idle speed, for example, 8800 R. P. M., Fig. 2, with a small rate of fuel increase; however, from this speed to the top speed of'l2,700 R. P. M., the allowable fuel input increases more rapidly than speed.

The fuel input has to be controlled in relation to rotational speed and temperature so as to avoid stalling of the compressor. While thermal emciency is increased by increase in turbine temperature and the latter is increased with increase in fuel input, increase in fuel input requires increase in turbine speed, otherwise a compressor stall condition may be reached. In Fig. 2, operation should be kept below the stall line designated ab. From the latter view, it will be apparent that the allowable fuel input increases quite rapidly in relation to speed as the turbine temperature is increased.

Fig. 3 shows the relation of thrust or power to rotational speed for different temperatures. A given power may be produced over a range of temperatures, the speed being increased as the temperature is reduced for development of the same power.

From Fig. 2, it is seen that the fuel input may be increased rapidly imrel'ationto speed, the temperature increasing, and that the temperature a function of fuel inputpand, :from Fig. 3, it will be .a-pparentthat the same power may be developed with-reduction inspeed aszth'e temperature is increased. Therefore, as torque increases as. the speed .is reduced for the same power, change in fuel/input may occur with a change in torque which is large in relation to change in speed.

with the turbine power input by varying the propeller .pitch :so thatiithe turbine may operate at a speed and at a fuel input giving the :best fuel rate, the optimum being afuel .input giving the highest "temperature practicable "without stalling for any given speed. 7

Therefore, as change fuel input with increase in temperature is felt largely'as a change "in torque, a measurecf torque constitutes a primaryfactoruseful to control propeller pitch 'and fuel input,.supplemented by speed and temperature controlling efiects. Further, with a change in operating conditions, a change in torque occurs immediately, that is, it anticipates change in speed, whereas, speed and temperature changes being influenced by inertia effects, necessarily lag. Hence, stability of :control is promoted by using torque to stabilize the temperature and speed controls. j iReferring generally to the. main control system, fuel is supplied to the 'atomizers 22.01: the com- :bustor'tB by tmeans,-including a booster pump 23, afilterli, a feed pump .25, a-fuel control, at 26 and av dump valve .21, to a manifold 28 or the like supplying the .atomizers. The fuel fiowconltrol device, at 26, has a motor 29 operative to vary the fuel input.

Mechanism, at 30, is operated by a controlling :motor 3! to vary and reverse the propeller pitch.

Controlling inputs are supplied to the control mechanism, at 32, from the torquemeter 33, interposed in the driving connection between the turbine and the propeller, preferably between first and Second stages 12a and 12b of planetary reduction gearing, from a tachometer 34, and from turbine temperature-responsive means 35, and outputs are supplied from the control mechanism to control operation of the fuel control motor .29 and the pitch control motor 3|. In

. addition to the torque, speed and temperature inputs, the control mechanism, at '32, also receives inputs from the condition and power levers 3B and?! arranged in the cockpit and operative to vary the-settings for the controllin inputs.

Referring to the emergency controlling system, Figs. 1 and 11, the apparatus, at 38, includes a normally ineffective component which operates automatically in response to speed to vary the pitch'of the propeller, the manual control '39 associated with the emergency fuel control apparatus, at 61, then being operated to vary the fuel flow to the combustor atomizers, the apparatus, at 26, having a shift valve .0, which is shifted to cause flow from the feed pump "25 to take place through fuel-air ratio controlling apparatus 4 l, responsive to fiow conditions occurring 'in the-compressor, liquid fuel being discharged from the apparatus M through thedump valve :to the atomizers.

So long as the main control system isinropera- -.tion,:pressure or potential is maintainedin the line 43, pressure or .fpoten't'ial in the branch 43a 'rendersithe emergency .speedzanii hydraulic pitch control inefiective and renders "the main :pitch control apparatus effective, and pressure, or 1400-- tentialin the branch 43'?) positions the shift valve "-ilfi so that fuel is supplied through the control .apparaituatat 26, so as to flow through the valve controlled by themotor 29,:ancl the .dump valve to the atomizers.

i-Io guard against the .consecui'encesof certain operating econditions., -control is automatically changed over from the :main to the '-:emergency "system. Among such operating-conditions are. failure .of main control power; over-speeding; over-temperature .lasting a predetermined time; and sudden loss of fuel pressure :during take-.ofi. Inresponse to any of these conditions, means, such as diagrammatically and collectively. :indi- -catedat 1114 (Fig. 111.), is "operated toreduce the potential the line as, such reduction resulting in the speed and hydraulic, pitch. control taking control of the propellenin interruptmg' the =driving connection between the .pitch :controltmotor 3!. and thepropeller, and in .rnovement ef the shift valve 49 so thatilowicf :fuelunder control of the manual means. 39 takes place :through {the V fuel-air ratio apparatusgari it'othe atomizers.

.As' the nseam -35 responsiveztolturbine tem- 'perature is preferably-"constituted byan arrangement 'oftthermoc'oupl'es :ag'a torquem'eter of the electric type :giues vtery.rapidresponse, I prefer to use an electric tachometer 34 and to provide electrical sources :of :C.; and C. power provided, respectively, by the :D. (3. generator 46 and the inverter 41, .the latter operating 'to develop A. C. power .at high :tr'equency, for :example, 460 cycles per second. With electrical inputs, the control apparatus, at 32, is-preferably of the electronic typawvhereby smal'l changes in electrical inputs from the ftorquemeter, the tachometer and the thermocouple arrangement may be used to :control 'd-irect and alternating current power received from-the generator 46 and theinverter 6? so asto control the direction and magnitude of D. C. power supplied to the fuel control motoriil andthe pitch control motor 3!. The electrical apparatus, at32, is shown diagrammatically in a viewcomposed of Figs. 4A, 4B and 40 arranged side-'by-side, the same-conductor from figure to figure being identified by the same letter.

In general, the voltage responsive or electronic control apparatus, at 32, includes twin, vacuum tubes, at-EO, 51, 52 and 53 (Figs. 4 and 5) subject to electrical inputs from the torquemeter, the

thermocouple arrangement, and the tachometer to control power supplied to the fuel control motor 29 and to the pitch control motor 3! so that, with either changing turbine-torque or tem- 'peratur'e, the motors ZS-and 35 are operated to changethe fuel input and the propeller pitch, an increase in either torque or 'temperaturebeing accompanied by a decrease in fuel flow and propeller-pitch. On the other hand, with change in turbine speed, the motors are operated'to change the fuel flow and pitch oppositely, an increasein speed causing reduction in fuel flow and increase in pitch. To reverse the propeller pitch and to control the reversed pitch, torque and speed control of thepitchcontrol motor are replaced by manual control.

vThe vacuum tubes, at .56 and '51, are effective to control directlygthefuel control and pitch control motors 29 and 3 4, :such tubes .not only receiving the torque load control voltage but also algebraically added torque output, speed and temperatur voltages. The tube, at 52, receives input from the thermocouple arrangement and impresses its output, added to the torque voltage, through the speed control, on the tubes, at 50 and so that either torque or temperature changing in an increasing direction is effective to reduce both fuel input and propeller pitch and the tube, at 53, receives input from the tachometer and impresses its effect on the tubes, at 50 and 5|, so that changing turbine speed changes the fuel input and pitch in opposite directions, an increment of increasing speed reducing the fuel flow and increasing the pitch and vice versa.

Since the electronic network involves fuel-control and pitch-control servo-motor control tubes 50 and 5|, each having grids 2 and 6 whose potentials are normally balanced with the potential of each grid 2 subject to change because of torque, temperature and speed changes, a brief consideration of the controlling network and its operation will aid in a ready comprehension of the ensuing detail description. The grids 2 of the fuel-control and pitch-control tubes 50 and 5| are connected by conductors H6 and M! to the outer ends of the series-connected resistances I39 and I40 in the bridge connection of the speed bridge circuit, at l 34, containing the vacuum tube 53 as one of its arms. An increase in speed increases the tachometer voltage impressed on the tube 53, thereby changing the impedance of the tube arm of the bridge and unbalancing the latter to lower the potential of grid 2 of the tube 50 relative to that of its grid 6 and to increase the potential of the grid 2 of the tube 5| relative to that of its grid 6, the unbalanced grid potentials causing servo-motor operation to reduce the fuel input and increase the propeller pitch until, due to potential changes of the grids 6 effected by servo-motor operation, potential balance of the grids of each tube is restored. Since the torque and temperature network outputs are applied to the midpoint |4| between the series resistances, changes in torque and temperature produce like, instead of reverse, operations of the servo-motors.

The temperature network includes temperature and over-temperature control bridge circuits, at H56 and at |9|, having as arms thereof left-hand and right-hand portions of the tube, at 52. Increase in thermocouple output varies the tuning of oscillator circuits including the lefthand and right-hand groups of tube elements to vary the impedances of the latter in the bridge circuits. Considering the bridge, at I66, increase in temperature reduces the tube element impedance, thereby making the potential at bridge slider ||3 lower than that at the cathode 3; and, as such slider potential is applied to the righthand cathode 5, the impedance of the tube arm of the bridge |9| is thereby reduced, making the potential of its slider I99 lower than that of the cathode 6. As the slider l!!!) is connected to the series resistance midpoint MI, increase in temperature results in decrease in potential of the grids 2 relative to the grids 6 of the tubes 59 and 5| for servo-motor operation to reduce the fuel input and propeller pitch in response to increase in temperature. In addition to the bridge |9| operating similarly to the bridge I66 and adding its effect to that of the latter, its primary purpose is that of over-temperature control, it overriding when required, all other factors of control to reduce the fuel input and propeller pitch,

An increase in torque reduces the potential at the torque network slider 84. As such slider is connected, by the conductor 91b, to the cathode 3 of the tube 52, torque changes will be reflected through the temperature and speed control networks to the grids 2 of the tubes 50 and 5| to reduce the potential of such grids relative to that of the grids 6 to reduce the fuel input and propeller pitch in response to increase in torque.

As will be hereinafter pointed out, the network has settings which are operative to change the torque, temperature and speed levels. As long as the torque, temperature and speed levels remain unchanged, the network is balanced; however, balance is disturbed by variation in these operating characteristics or by adjustment of torque, temperature and speed settings. Deviations are minimized by the regulating operation of the system and the settings are operated to raise-and lower the regulated torque, speed and temperature levels. Network unbalance is followed by changes in fuel input and propeller pitch to bring about such relation of turbine torque, temperature and speed conditions that the balanced relation is restored.

Changing torque, changing temperature and changing speed are factors which act to adjust the fuel input and pitch to restore balance at any power level. Because of the tendency of changing torque, changing temperature and changing speed to adjust the fuel input and pitch to produce torque, temperature and speed conditions for restoring balance, it will be'apparent that, at any torque, temperature and speed level, any tendency to departure therefrom is resisted.

Preferably, the fuel control vacuum tube, at 50, and the pitch control vacuum tube, at 5|,respectively control Ward-Leonard, or voltage control, fuel control and pitch control drives, at 54, and, at 55, the tube, at 50, controlling the fields 51 and 58 of the generator 59 of the fuel control drive and the tube, at 5|, controlling the fields 60 and BI of the generator 62 of the pitch control drive, the generators being driven by the motor 56.

In the steady state condition, the opposing field windings of each of the generators have currents supplied thereto by the tubes, at 50 and at 5|, shch that the opposing magneto-motive forces in the generator fields are equal, with the result that the fuel control and pitch control motors 29 and 3| remain stationary; however, with variation in any of the factors of control, the currents supplied from the tubes, at 50 and at 5|, to the generator fields cause the motors 29 and 3| to be operated to vary the fuel input and the pitch in the manner already pointed out.

In addition to the already-described electrical equipment, embodied in the control apparatus or electronic control box, receiving inputs from the torquemeter the tachometer, the thermocouple arrangement and from the D. C. source, such apparatus, includes a power transformer T-l receiving power from the A. C. source and delivering power through windings and rectifiers to the tubes already described as well as to other components, such as supplies of bridge circuits, of which the rightand left-hand parts of the tubes 52 and 53 form impedance arms, and of the torquemeter, which will be immediately described.

torouemeter, at 33, is of the electric or magnetic strain gauge type and it preferably inolves the structure and operative principle such disclosed and claimed: in the patent of Bernard F. Langer and Frank W. Godsey, Jr, No.

ze cc'z ecs 12,459,17-1 ,and, as indicateduit has ag.pair:nf:.coi1s 1 3 and T -=4 connected in such a manner that they both; produce fluxin the same direction.

The fixed coils, VIP-3 and I -4, encompass spaced and interfitting serrated jportionswof :a pair of spaced collars and an intermediatewsleeve -(Fig. =6), the collars and the sleeve each being -fixedly secured to thedpower shaft, for example, the :section 1 la thereof between 1 the reduction fgear stages, so that torsional defiection :of the *setofserrations to decrease and that :at the .other to increase.

-With torque applied'to the power shaft, the

gap-width at :oneset'oi serrations diminishes slightly While that of the other increasesslightly and asithe 'coils' -are supplied with A. Qrpower, ior example, 400 cycles per: second, the impedance of the coil over the 'serrationisetlof diminishing lgap width increases while that of the other coil decreases. By :using a circuit which "measures :only the inductive reaction it ispossi'cle .to

measure the difierence ibetween the -air gap l :latterdue toitorque causes theigap Width atone widths-with a high: degreetof accuracy. Since the withgpositive torque beingtransmitted through i the '1 torquemeter, the ?'impedance of coil T-r3 is greater than that 'of T and the voltage drop -:across :T-filisigreater than the dropz-across T-fi. JDuringthepart of the 'cycle'when' the top of--63w is-positive relative tc the -slider"65,- 1the:connection between T-3 and T- 'l is negative relative to the-slider. During the part of the-cycle when --the top of G3wis v negative," the oppositetis true. Hence, a'rralternating voltage Whose phase angle 'and magnitude, relative ito the voltage in 16320, "depending upon the value: of unbalanc between T43 :and T-t': is applied' acrossthe primary 660i transformer T-2 having the secondary c1. To simplify :furtherdescription, it is "assumed that the. positive part of the cycle occurs-When the :top of 631.0 is positive, and" the negative part when wlevel sand-to :isolate Ethe torquemeter coils from :therest-otthecircuit.

The signal induced :inthe-secondary of-wtrans- .former T-Z is'rrectified and ephase=demodulated by-means-i-ncluding'the torcue bridge,-at-B8, the

-1atter comprising rectifiers fi9, "H3, Hand- 72, and

resistances "i3, 14, and 'lfi'rand thezero-setting "potentiometen'it. The endsofthe secondary 4'51 and-cor the supply winding 7911; are connected icy the bridge;- at- 58, the secondarywindi-ng connec- 1-2 tifier it and -i the resistance d6 *while -the other includes the rectifier :69, the :resistance :t4..-and

the portion of -.zero.-setting potentiometer 'l-8:-.re-'

.sistance abovetheslider 11. :One lowercarmzim eludes the rectifier i2 and .resistancelfi, and the other rectifier I l the resistance 13 and thesl ortion of the potentiometer resistance below :the

slider. 7

During the-positive swing, the top of winding 19w is positive, :current fiowing ltherefrom through rectifier), resistances 16 and 1:5:and vrectifier 72 only. Rectifiers iii-i land 1 l.;are.:b1ocked .by the reverse voltage. Sincexthe -'winding'-1:9w..-is designed so that its voltagelis'always at rleast twice the maximum voltage which -canvbeede- .velopewacross :the-rsecondaryvfil of transformer LI -.2, current canrnever fiowrthrough'thabl'ocked -rectifiers.

' Consider -:-that the deft-ends or" both :windings #66 and 5710fthe-transformer T-Z areeithenposi- .tive or lnegative'zat the :same :time, themszdurwing-ithegpositive :sWing, the left end ;of theses-- :ondary:isrpositive. In addition to themurrent ..from winding *tiiw eurrent flows'from .tli'eacenter: tap 853 ofthe secondary :6? down tthroughathe .setting=:resistance 8i :and the potentiometerrre- "sistance--t3, with which the slideri 84 cooperates, :to-the. center tap 860f .the'windingtiiw; theiupper part of the windin'g'isic, the: rectifier T0, .resistance-?6,- and-back to the rightendzofithe second- Cary-6i.

During-the. negativezswingyscurrentsffiows from the center: tap of secondary iil-idown through resistances '-8l fiend-:83, therlower .halfcof wiriding .1910, .theu-rectifier ll, ."resistance :1 3, :'.the lower part .of'resi'stance J8, and loack -to the ;l'eft'=.end .of the secondary fi'l.

Thus, when; positiveztorque.:isrrbeingxtransmit- :ted bythettorquemeter 33, tithe top :df :resistance .83 is ithejgpositivewend iduring-bothhalvesmf the .A.-.C. cycle.

The torque reference voltage winding *BBw ha's its ends connected, through thezrectifiers '9 and 90,:tothe positive supplyzsideffi l ot the :reference circuit-whose negative return'sidew'fiz' iszconnected .to themidpoint-Btof the winding. potentiometer 94 has the ends of its resistance connected to-opposite sides of the :reference :circuit and the slider :of the potentiometer includes the "portionof-theresistanee ofithedatter 'inthe torque output: circuit comp1'ising-. the-I conductor-Q 5, :the :portion cofiresistance of potentiometer 83 above thesslider fl; the conductor 97 TCOIIIIeCtBdTtO dzhe slider wandebranches of such :conductor tome-described; and the return side 92. V

fIfhegpotentiometer94, provides the torqu'efref- .erence voltage for :the :contro1tsystem,:.its "slider :mak-ing it possible.toeasilyzadiust forzero' torque voltage;- .flihe voltage :of TtheitOIlIlIE :measuriug circuit a across the iportion iof the itresistance :of potentiometer 283 above tlie slidrs 84 Chucks ":the voltage-10f the potentiometer 94 :in'ithe output circuit-arid to the 'leitfof .s1ider"95 when theplant has "positive torque xoutput and adds when the plantris absorbing torque. THence;withiincreas'- ing torque,:as-'currentfflows fromi the left-hand end :of "94 'to =the'-'s1id'er"'8c; the potential -at"th-e latter decreases. I On *the 'other hand, with idecreasing torque, the "contrary 'TiS" true, "the slider potential increasing.

From" the foregoing, it willbe *apparent'that there :is provided aitorque voltagewhich' varies :uplnr :down: fromttherzreferenceevoita gefimilinear proportiontto thevariatioiriin fturbineltcroue.

Further; :it Tzbeeseenidshat ilie miag'nttude '13 of the output voltage variesin direct proportion to the voltage supplied to transformer T-I. The proportional change in output voltage with changes in torque level is constant. In order to obtain a torque indication, it is necessary to match the output voltage with voltage of potentiometer 99 whose left end is connected to the supply side 9| of the reference circuit, which is supplied from the transformer T-I by means of the secondary winding 88w.

The torque output circuit from the slider 84 of the potentiometer 83 to the left end of potentiometer resistance 94 includes the conductors 91 and 91a, the slider 98, the portion of resistance 99 to the right of the latter and the return 92. Such circuit includes the winding of the relay, at I00, controlling a motor IOI for moving the slider 98. The resistances l02a, I021) and I020 form a velocity feedback network for stabilization of the circuit. For zero torque, the slider 98 is positioned by the motor depending upon the setting of the slider 95 of potentiometer 94.

As the output torque of the turbine increases, the slider 98 of the potentiometer 99 moves to the right, thereby operating the visual indicator IOIa, thus decreasing the voltage output of the potentiometer to balance the decrease in output from the torque output circuit.

Neglecting for the moment the eifect of speed and temperature signals on the operation of the control, the operation of apparatus sofar described for varying the fuel input will now be considered. The output of the torque circuit is from the slider 84 of the potentiometer 83 to the left-hand end of the potentiometer 94. The torque control circuit for the fuel input motor 29 may be considered as beginning with the setting rheostats I05 and I05, which function to put position of the power lever 31 into such circuit. The output from these two rheostats is supplied by the leads I05a and Iota to rheostats I01 and I08 which form the altitude bias on sensitivity of the controlling circuit, a bellows H0, or the like, being eifective to move the sliders along the resistances of the rheostats I01 and I08.

The voltage developed between the sliders of the rheostats I and I08 is applied directly by the leads Ib and I061) to the position feedback potentiometer III for the fuel input valve actuator operated by the motor 29. The slider I I2 of the potentiometer I I I is connected, through the velocity feedback resistance networks H3,

H4 and H5 to one of the control grids, the grid- 6, at the right side of the tube, at 50. The other control grid 2, at the left side of such tube, is connected, through the lead I IS, the speed control and the temperature control to the torque output slider 84, as hereinafter described. Thus, the torquemeter is a torque regulatorin which the voltage shift set in by operation of the power lever determines the torque level at which regulation occurs, the torquemeter output voltage serving to control the fuel and pitch to minimize torque deviation at the adjusted point.

Assuming that the sliders of the rheostats I05. I06, I01 and IE8 are fixed, then the operation of the circuit is as follows: The voltage drop across the potentiometer III and the voltage level at the bottom of the latter will be in fixed relation to the voltage applied by the potentiometer 94. Assuming that the circuit is in balance at some torque level, if a step of increase in torque occurs, this will decrease the voltage at the slider 84 of potentiometer 83 relative to the voltage at the left end of the resistance of potentiometer 94'; and with the grid potential fixed by adjustment of the torque setting potentiometers I05 and I06, the increase in torque acts, through the temperature and speed control, to reduce the voltage of rid 2 relatively to that of grid 6, in consequence of which the right section of the tube, at 50, will conduct more current than the left section thereof, and more current will flow through the lower field winding 5'! of the generator 59 of the fuel control Ward-Leonard drive, at 54, than through the upper Winding 58 thereof.

Since the circuit was in balance at the beginning, the same amount of current was flowing through both generator windings; and, in this conditiomno voltage was generated in the armature of the generator. However, as the torque changes, the resulting unbalance in current between the two field windings, causes voltage to be generated in the armature of generator 59, and thus causes rotation of the fuel control motor 29, the latter motor rotating to move the slider 1 I2 downwardly, and decrease the fuel input, the slider I I2 being brought to rest with the voltages applied to the grids '6 and 2 of the tube at 50 balanced and the circuit is restored to balanced condition. Thus, the input of fuel is changed to correct for the torque change. The opposite action will occur if the torque falls below the set point.

If the pilot wishes to increase the output of the engine, he operates the power lever 31 to move the sliders of the torque setting rheostats I05 and I05 to the left, thereby decreasing the voltage level at the bottom of potentiometer I I I. To rebalance the network, pursuant to said power lever movement of the sliders of I05 and I06, the fuel input control motor 29 is driven in a direction Which moves the slider H2 of potentiometer I II upward. Since this motion increases the fuel flow, it also increases the power output of the turbine. It should be noted that, because the increase in torque tends to cause a decrease in fuel flow, the motion of the actuator does not proceed as far as it would if there were no change in turbine torque.

Control of the tube, at '5I, of the drive, at 55, for the pitch control motor is similar to that of the tube, at 58, of the drive, at 54, for the fuel valve control motor. As with the fuel control motor, the controlled circuit may be considered as beginning with the torque setting rheostats I 05 and I09. The output of these rheostats is applied to the sensitivity biasing rheostats H8 and H9, the bias thereof being under the control of the flight velocity and atmospheric density bellows I20. The voltage developed between the sliders of the biasing rheostats is applied, by the leads I 050 and I 060 and through the reverse pitch relay, at I2I, to the position feedback potentiom eter I22 of the pitch control motor 3|. Under normal flight conditions, the operation of the remainder of the circuit is the same as that for the fuel valve control motor.

To recapitulate with respect to the torque regulating network, the torque setting or level is varied by changing the setting of the potential-rangeshifting potentiometers I05 and I05, whereby the potentials at the sliders II! and I23 and consequently at the grids of the tubes, at 50 and 5|, are influenced for motor operation to change the input of fuel and propeller pitch; however, the

change in fuel input brings about a change in torque in consequence of which the change in potential at the torque output slider 84 and, there- -rs ifore at-theigrids;of the tubes,.-at-:50. andiie'l, tend to :produce motor -motion.:opnos'ing :such :motion in consequence of ithe: change in setting.

"The torque output voltage at: the slider 35 pew formsa regulator function-to minimize deviation inutorque at anysetting. As long as the torque tdoesnotchange relative 'toxthe torque setting, .the sliders TI I'Zandsl=23of therpotentiometers I I' I and 1sI22:are positioned clepending on .ithe'position of slidera95 of the: potentiometer 21%. Assuming. an increase I in.torque,zthe 'potential .at :slider 135 :de-

creases, whereupon .two .operations'take place. Thesmotor. Iill :movesth-e slider 59.8 to decrease "the-voltage output of the potentiometer as a to :the torque change,:reduction.in torque resulting I in increase in potential at the slider 8 Control of turbine rotational speed and of atemperature is accomplished by adding .to and Subtracting-from rthe ouput voltage "from the torque measuring circuit. The controlof temiperaturerasvvell as'thatof torque, is accomplished by movingthe-fuelinput control motor-28 and the pitch .oontrokmotorzBI .soathat, if either the temperature :or the 'torque increases, the control motors are operated'todecrease the fuel input and I thex propelle'npitch. ilnrthe case of enginespeed, "however, ,the control motors .must :move in opposite-:gclirections; that is, if. the turbine rotational p ed tiinclteases, the Jfuel input control motor moves, in a: direction.to decrease theffuel flow while the pitch control motor moves.inthe directionto increase the propeller pitch.

Gonsicleringfirst the operation of the engine rotational speed control, .thev output: of the tachorneter :generator 34 is applied, by the circuit 34a, across the resistances I24, I25.-and I26,'I*24 being the setting-potentiometer 'whichputs the position of :condition lever :36 into :the circuit, I25 the maximum 5P. M.-:setting resistor, and *I-2-6.-the pilots-1R. ;P.'. Mztrimmer, the latter being :in the-cockpit ,aandnsed to :synchronize power units 7 in a :multiplee-unit;installation. The setting potentiometer I21! nuts the positionof power lever 3 'I into thecircnit. The voltage developed between the sliders :1 261a and 4211a of the potentiometers I26 and I2! is the control voltage which is :fed :into'the electronic circuit'by the leads, -I 29 and I30.

'Ehe,actua1.,-R. ;-P. M. control circuit consists of ,two;sectionS, oneproiducinga :Voltage which I is proportional to --.th e R. --P. error and the other a voltage which is proportional to the integral of; R. P. M.-error.

Considering first, operation of the R. 'P. M. control circuit without the integrating section being effective, the tachometer 34 provides, by the conductors I29 and :I3fl for the bridge, at iflkanfinput voltage, dependent upon rotational speed and the setting: of the 'potentiometers and which is supplied to-the grid 4 of the righthandsection .of the twin vacuum tube, at 53, that -.-section forming 10118 -:o f the arms of the .bridge,- .at t34,-the otherzthree armsbeing comprised .by the; resistance 35,:the-wportion of the resistance HIS-above ;the:slider; [31,; and? then-poi.-

tion: jOfithB resistance #35 belowctheelider. "tithe cross or outputconnecition:of-therbridgei:includes the-voltage;divider,;;at L38, comprisingvupperaand lower resistances I33 and :IAB joined and having an intermediate; point I4 I connected .by the; conductor I42 :to the temperature; control, vasiher inafter ;;pointed out. The .uppengend ;,of themesistance I39 is connected to,the conductor 111,6 leading to the left-rhand. ,grid ",2 ,of the fiuel contro1 vacuum tube, at 53, and thebottom end of the lower: resistance .IAIl is connected to acon- ,ductor I-4'I -including anormal ly ,closed contacts I 48 of the relay, at IZ-I and leading, to :theggrid 2 of the pitch ,control vacuum tube, at :5 I

With increasing .speed, the potential -,Of1-th grid 4 of the right setof tube elements ,of the vacuumtube, at..53, is raised and the resulting potential of the bridge .cross connection causes the bottom end of the voltage divider, ,at I3B, to .-be positivegrelativexto the upper ther o in consequen e .of -Whi. h.the.v 1ta es of thegrids 2. of the vacuum tubes, at35il and 5 I, are changed to reduce ,the 7 fuel inputgand to increase the propeller .pitch to oppose-speed chan In addition t the velocity .or speed re p ns o rating on the fuel input and pmpcllenpitch to pp error or dwiationinsneesl.from th setting, there is provided means securing ,.a c.orrecting eifect dependent nppnthe error oizdeviation magnitude, that .is, an; arrangement which performs an integrating function.

Therefore, as both the "left grid 1 andthe right'grid 4 are connected ,to the supply line I28, when'the rotational speedsuffices to provide a plate current ,in the left set of tube elements of the tube, at 53, to energize the -win dir-1g"I 5-I adequately to pull down the armature I-2,-'-the powercircuitfor the motor I 53is closedthrough the voltage divider ISA-and the motor operates to move thebridge arm slider I37 upwardly to.

transfer resistance from the upper arm to'the lower one of adjoining armsof the bridge.

As the motor I53 has a velocity feedback network comprised by resistances i55, I56 and IEI, of which the resistance isin series with the motor armature and the resistances I55 and -45"! are in shunt therewith andiforma voltage divider whose intermediate point is connected, by :a conductor I58 and cathode resistor,--to .the. cath- :ode=3 of the left section of the-'-vacuum;;tube '53; there is introduced-into the; cathode acircuit a voltage-which is proportional-toithe rotational .speed of the motor'and 'thewvoltage is always in a direction r tending :.to stop the motor.

Therefore, .when'the rotational speed increases above a1set point, the motor I53 operates i .move the slider I31 upwardly to transfer; resistnc 'ffrom h pp r abri ge :arm i o th brid a1:m:at=.a rat whic z epmpo na it th err r b tween :th -aact al "and :se speed. This --motion tends to a raise the woltage of'the slider relative to the :voltage of the; plate 50f the right ;-s ectionof the tube 53. Thus, the'left, or integrating sectionof zthetube produces a correction voltage in the-same direction as the right section thereof.

The motor I53 is reversed dependent-upon engagement ofmthearmature contact I52 with either the fixed upper contact I52a or. the lower one I52b. The operative engagement with the lower contact has justbeen described. When h 1 91 .6 001 1531. n f n'th 1 1017 1 i 1i. in a ,directiontolowe h sslide .Asth armature-contac 5 gis imovedzbvthe o p sin for es of :..t-h 1; p1tine IEJa-andthe magnet-wind- 17 ing H, the moved contact will operate in a hovering manner to control the motor to shift the bridge slider slightly up and down, whereby the bridge arms are adjusted to vary the output voltage applied across the resistance of the voltage divider, at I 38.

As the motor armature is connected in the cathode circuit of the left section of the tube, at 53, a voltage proportional to motor speed will be applied to the cathode circuit, which is so arranged that this voltage is always in the direction tending to stop the motor. Thus, the motor will run at a speed which is proportional to the deviation of the control signal from a set value, and it is this proportional speed response of the motor I53 that makes the circuit produce the integral of rotational speed error. Hence, as the motor I53 moves in a direction determined by and at a speed dependent on the deviation and as the bridge is adjusted thereby to provide a correction voltage acting in the same direction as the first correction voltage, such an arrangement operates as a compensator to minimize deviation of turbine speed from the set value.

Temperature control utilizes voltages supplied by the thermocouple arrangement 35 so that an increase in temperature tends to decrease both the fuel input and the propeller pitch. To this end, by way of example, there are provided controls, at I59 and, at I60, responsive to temperature and to adjustment of their levers I6I and IE2, respectively, to vary the tuning of the high frequency oscillator circuits, at I63 and at I64, and including the right and left sections of the twin vacuum tube 52.

The first control, at I59, is effective, with torque and speed, continuously to control fuel input and propeller pitch, whereas, the second control, at I60, in addition to aiding the first, protects against over-temperatures, the latter control being operative, dependent upon the speed setting and the attainment of sufficient temperature, to override the other controls and restrict the fuel input and propeller pitch. The first control lever I6I is moved by the power lever 37 and the control lever I62 is moved in response to tachometer output, as hereinafter described.

Control of the set point of the control, at I60,

as a function of engine R. P. M. is necessary because of the stall characteristics of the compressor. Compressor stall makes it necessary to limit the turbine inlet temperature to a value slightly higher than 1360 R. when the engine R. P. M. is less than 8800. When the R. P. M. is reached, the turbine inlet temperature may be raised to 1660 R.; and when the speed reaches 9800 R. P. M., the temperature may be raised to 1960 R., these being approximately the engine speeds at which the set points of the control, at I60, will be changed.

Referring to the first temperature control, at I59, and the oscillator circuit, at I63, which includes the left part of the vacuum tube, at 52, such left part of the tube also constitutes an arm of a bridge, at I66, and whose other arms are comprised by the resistance I67 and the adjacent portion of the resistance I68 to one side of the slider I69, the portion of the resistance I68 at the other side of the slider and the adjacent resistance I70, and the resistance Hi. The bridge has an output or cross connection joining the slider I69 and the cathode 3 of tube, at 52, the connection including the resistance I72 with 18 which cooperates the slider I73 to constitute a sensitivity potentiometer.

The slider I73 is connected, by the conductor I74, to the over-temperature control, that is, to the cathode 6 of the right section of the tube, at 52.

Increase in temperature changes the tuning of the oscillator circuit, at I63, to increase resistance of the bridge arm formed by the left part of the tube, at 52, in consequence of which the cathode "3 is made positive with respect to the slider I73; and, as the cathode is connected, by the conductor 97b, to the slider 84 of the torque potentiometer, at 83, increase in temperature is effective in the same manner as torque, that is, such increase brings about reduction in fuel input and propeller pitch.

With respect to over-temperature control, its

oscillator circuit, at I64, operates in a similar manner except that its control, at I60, instead of having the effect of power lever position set therein by operation of the lever I6I, as with the control, at I59, it has its adjusting lever I62 mechanically connected to magnetic operating devices, at I75, and, at I76, which operate upon the attainment of predetermined speeds, as determined by the setting of the resistance I77 in the input supply from the tachometer to the relay, at I78, and upon the spacing of a pair of fixed and spaced contacts of the latter. Therefore, in addition to temperature, the circuit, at I64,Jde-

pends on speed so that, as speed is increased, the

temperature point or temperature points at which the over-temperature control becomes effective are raised.

The relay, at I78, includes windings I79 and I8!) and a biased armature I8I. As long as the speed is below a given value, dependent upon the resistance and relay settings, for example, 8800 R. P. M., the armature is biased to complete a circuit including the magnet winding of the device I75, whereby the lower end of thelever I82 is pulled to the right against the force of a spring I63 in which position, the control is set to restrict fuel input to limit the temperature to a desired value, for example, slightly higher than 1360 R. as long as the speed is below .8800 R. P. M.

With increase in speed and increased energization of the relay windings, the armature is pulled away from the left contact of the relay, breaking the circuit for the device I75, whereupon the spring I83 is effective to pull thelower end of the lever to the left. As the lower end of the lever I32 is moved from the extreme right position to the extreme left position, such motion is transmitted by suitable linkage to the setting lever I62 of the control, at I69. 1

The effect of adjustment in response to speed is to raise the temperature point at which-the control, at I60, is effective to bring about overriding of the other controls and restrict the input of fuel and the propeller pitch, that is, the temperature is limited to a higher value, for example, 1660 R, when the rotational speed of 8800' R. P. M. is reached.

With further increase in speed, the biased armature I8I is pulled to the right engaging its contact with the right one of the spaced contacts of the relay to complete the circuit through the magnet winding of the device 76, energizetion pulling the upper end of the lever 482 to the extreme left to operate the linkage to move the lever I62 of the control, at i66, to a higher temperature point so that, when a speed of 9800 is 19 reached, the temperature may be ira ised to 1960- R. a Thefright part of the twin vacuum tube, attZ, forms a component of the 'over-temperature oscillator network, at 15s, and it constitutes ene arm of a bridge, at I9I, whose other arms are provided by the resistance I32, the resistance I35 i and the portion of the resistance I35. to the left voltage divider, at I38, as a conductor Il t connects the slider I13 'of the potentiometer of the bridge, at I66, to thecathode 6 of the right part of the tube, at 52, and, as the cathode 3 of the tube is connected to the torque potentiometer slider 84, provision is thereby made for algebraic addition of torque output, temperature and speed voltages for the exertion of .controlling effectson the tubes, at E and 5|. In other words, torque control acts through temperature and speed control to influence the potential at the grids of such tubes, resulting in operation of the fuel and pitch control motors until grid potential balanceof the tubes is-restored. a

a The over-temperature control comes into play and overrides all other factors of control to limit fuel input and pitch to avoid predetermined temperatures' being exceeded until predetermined speeds are reached, the over-temperature response changing the voltage relation of the bridge slider I99 and the cathode 6 and applying voltage through the conductor I42 to the intermediate point HII of the voltage divider and thence to the grids of the tubes, at Siland 5|, to bring about restriction of fuel and pitch. Thus, in addition to the controlling system being effective to provide for an operating temperature which increases as the speed increases, provision is made for temperature and speed limiting the fuel input and pitch so as to avoid stalling of the compresesor.

In the electronic control box, indicated at 32, the condition lever 36 is connected to the slider 12% of speed setting potentiometer I24 and the movable contact of switch 294. Similarly, the power lever 31 is connected to the slider I210;

of speed setting potentiometer I21, the setting lever IGI of the temperature control, at I59, the movable contact of switch 205, the sliders of rheostats I55 and I96, and the setting slider 265 of resistance 208 whose ends are joined to opposite sides SI and 92 of the voltage reference circuit.

In the circuit diagram of Fig. 40, the rectangle marked off by dash lines indicates the cockpit .in which the condition and power levers and the tachometer circuit resistance I26 are located. In this View, movement to the right of the linkage marked Condition lever or movement of the linkage marked Power lever to the left is equivalent to moving either of these levers to a 7 higher angular position on its quadrant. The proper operation of these levers for plant operating and flight conditions is graphically indicated by Figs. '7 and 8.

Assume that the power lever is in its zero position with the slider I21a. at the left. end. 0t r 20 sist'ance' I21, the full effect of the voltage change due to the motion of the condition lever slider I 24a along the resistance I24 is felt in the R. P. M. control circuit. Thus, the condition lever produces its full effect on the R. P. M.

setting. I I

If the power lever slider IZIa were at the right end of resistance I27, moving the condition lever would have no effect on the R. P. M. setting. This is exactly the case when the power lever is set for maximum plant output. 7

Similarly, motion of the power lever, has less and less effect on the R. P. M. setting as the condition lever slider l2 ia is moved further and further to the rightalong the resistance lit incident to movement of the condition lever 36 to a higher and higher position on its quadrant.

Actually, because of mechanism, at 2-95 (Figs.

9 and 10) ,.mechanically interlocking the levers, the power lever slider 421a cannot be moved unless the condition lever slider lzta is near the right end of the resistance I2 2. As the right end of the power lever linkage is moved to the left, the power lever slider I2'Ia is moved to the right, the lever IBi ofthe temperature control, at its, is moved upward, the movable contact of switch 235 is moved to the right, the sliders of rheostats IE5 and I66 are moved to the left, and the slider act is moved to the right along resistance 2%. Thus, when the pilotcalls for more turbine power, he increases the torque, speed and temperature settings.

As the right end of the condition lever linkage .is moved to the left, the slider IZta is moved to the right. Hence, when the pilot moves the condition lever to a higher position on the quadrant, he increases the turbine speed setting.

In order to go into reverse pitch operation, the condition lever must be in its maximum speed position before the power lever can be moved into the reverse pitch position. When the condition lever 35, is in its maximum position, the switch 266 is closed; and, with initial movement of the power lever 33 from the zero position into the reverse pitch range, the switch 265 is closed.

When the flight velocity of the airplane is below some set value in the neighborhood of knots, the flight velocity bellows 216 allows the switch 2H to close; and, if the condition and power lever switches are already closed, closing of the flight velocity switch ZI I, completes the circuit to energize the coil ZIZ to pull the core or armature 2I3 down to move the relay, at 52!, toreverse position.

Upon movement of the relay, at I2 I, to reverse position, incident to closing of the switches 29 and 235 by upward or forward movement of the condition lever and downward or reverse movement of the power lever and to closing of the switch 25! ,just as soon as the flight velocity is at or below a predetermined amount, the pitch control potentiometer I22 is disconnected from the normal circuit by opening of relay contacts 2M and 2i5 and it is directly connected, through resistances 2 I5 and 2 I I, to the reference supply by closing of contacts 2I5 and 2I9, said normal circuit including the contacts 2M and 2I5 and being suppliedthrough the power lever potential range-shifting potentiometer rheostats its and Hit, from the torque reference Voltage supply and return lines 9! and 92. This makes the voltage drop across and the voltage level at the bottom of the resistance of the potentiometer I22 directly proportional to the reference voltage and independent of the power lever positions. The grid 2 of pitch control tube, at 5i, is disconnected from the speed control voltages by opening of contacts I48 and it is directly connected, by closing of contacts 226 and the conductor em. to the slider 299 of resistance 258. Thus, the position of the propeller pitch control actuator is controlled directly by the position or" the slider 2525.

As the end of the power lever linkage is moved to the right, to a position of greater reverse pitch, the slider on 286 is moved to the left, decreasing the voltage between the slider and the left end of the resistance 2%. In order to keep the circuit in balance, the pitch control actuator must move the slider !23 of pitch control position potentiometer l 22. The propeller blades move in the direction of more reverse pitch in response to this action of the pitch control actuator.

When the pilot wishes to go back to normal operation, he merely has to move the power lever back into the normal operating range. This opens switch 225, deenergizing the reverse pitch relay, at i2i, whereupon the biasing means or spring [2m is effective to move the relay to reestablish the normal circuit connections.

During reverse pitch operation, the fuel valve actuator must accomplish the entire control of the engine R. P. M. Since both the temperature control of the torque control are set at their minimum positions, the speed control circuit must be capable of overriding the signals from both of these when the propeller is set for high values of reverse pitch.

Referring to the interlocking mechanism, at

28$, for the condition and power levers 3t and 3?, with both levers at the power lever is locked so that only the condition lever can be moved and the power lever remains loci-zed until the condition lever is moved slightly beyond 60. This provides for starting and bringing the turbine up to idle ground speed, say 8800 R. P. M. when the condition lever has been moved 60, and up to about 12,708 R. P. M. when it has been moved to from about 73 to 75. With the condition lever at the 73 to 75 position, the power lever may be moved through its full forward and reverse range; and, just as soon as the power lever is moved about 1 from 0 in the forward range, the condition lever is locked so that it cannot be moved below 60. When the power lever is moved about l in the reverse range of 20, the condition lever is locked in the 73 to 75 position.

Assuming that the main control system is in operation, provision is made for changing over to the emergency system in the event of certain operating conditions. The change-over should be eifected when the main control fails, as by failure the primary power supply; if a 5 per cent over-speed condition is attained, control should be transferred to the emergency system; persistence of per cent over-temperature for more than 5 seconds should be effective to transfer control to the emergency system; and a per cent loss of fuel pressure during take-01f should bring about the same effect.

Accordingly, in Fig. 11, showing diagrammatically a propeller blade whose pitch is varied either by the automatic main control or by an engine governor, the pressure line 43 is shown in the form of electric circuit 431', which, with the main control system in operation, is effective to hold the magnetically-operated valve in the position connecting the fuel control, at 26, for flow of fuel through the valve controlled by the motor 29 to the atomizers. The energized circuit 433: also supplies the circuit 43a to maintain the by-pass valve 223 of the speed governor hydraulic pitch control system open to break the connections of the hydraulic transmission to the propeller blades so long as the circuit $33: is. energized. Also, as long as the circuit 433: is energized, it is effective to render the pitch control motor 3| operative to vary the pitch of the propeller blades. Furthermore, the automatic control system motor is operative by means, including the clutch 225, for turning the propeller blades. Upon deenergization of the winding 43b, the spring 430 moves the valve 223 to connect the governor, at 38, with the hydraulic cylinder 30a for movement of the operating piston 301) against the spring 300 to turn each propeller blade I 4 about its longitudinal axis to vary the pitch. Upon opening the circuit, the valve dB is shifted for manual control of fuel input, the governor connection for controlling the propeller pitch is established, and the motor 3i is disconnected from the propeller blades.

From the apparatus described, it will be apparent, that maintenance of the fuel control and the pitch control for operation by the main control system is dependent upon the circuit 539c being energized. Therefore, to protect the plant in the event of the operating conditions above referred to and effect transfer of control from the main system to the emergency system, there are shown, diagrammatic features of control operating to secure this result. Upon failure of the primary power supply for the main control system, control of propeller pitch is transferred from the main control system by interruption of the connection between the motor 3! and the propeller blades and by rendering the hydraulic system 30 effective by closing the by-pass valve and by movement of the valve to to shift the flow of fuel through the fuel control valve operated by the motor 29 for flow through a passage controlled by the manual control 39, the fuel passing through the ratio control device 49 and then to the atomizers.

In the event of a 5 per cent over-speed condition, a conventional auto-stop or emergency governor, at 230, is operative to interrupt the circuit 43m. Such a governor is a common expedient in the turbine art. As shown, it includes a pin 230a movable outwardly due to centrifugal force to move the lever 23% to trip the latch 2300 normally holding the switch 230d closed against the force of a spring 23cc.

If there is an over-temperature of 10 per cent persisting more than 5 seconds then the overtemperature is effective to control a switch 21 to operate a timing switch 232 in the circuit 430:,

the arrangement being such that, with an overtemperature of magnitude indicated and persistence of such over-temperature for a short time,

for example, 5 seconds, the switch 232 will be operated to interrupt the circuit 43$, whereupon, as already indicated, control of fuel input and of the propeller is transferred from the main to the emergency system.

Likewise, when a loss of fuel pressure occurs to the extent of about 20 per cent during takeoff, the same result is eilected. To this end,- there is provided a switch 234 operative in response to altitude and to pressure of fuel supplied to the atomizers, the arrangement being such that, with low altitude or low flight velocity, indica- "tiv of conditions at take-off, a loss of fuel pressure to theextent indicated will "be effective to move the switch 23 to interrupt the circuit 43a.

While any suitable interlock may be used in connection with the conditionandpower levers 36 and 37, asshown in Figs. 9 and 10, the interlock, at 2&9, comprises a detent 238 cooperating with the condition lever and power lever disks or cams 23? and 238. The detent is biased by a spring 239 toward the disk 23?. ihe disk 23% has a recess 246 to receive one end of the detent with the latter retained against the force of the spring by the disk 23?. Upon movement of the disk 231 to the 60 position, the recess 2% comes opposite to the adjacent and of the detent to provide for withdrawal of the latter from the recess 2&0 suflicient to permit the arcuate surface 242 to move under the detent end, the terminal abutments 2&3 and 2% limiting such movement to from 0 to 80. Upon movement of the condition lever to the 73 to 75 position, the detent enters the deeper recess 245 permitting of movement of the power lever over the range from +80 to 20; l, the surface 2% engages and upon movement from 0 to the adjacent end of the detent to lock positively the condition lever in the landing or 73 to 75 position.

Operation The apparatus described operates'as follows:

1 Pursuant to movement of the condition lever 36 from its 0 position incident to starting of the plant, such lever is moved further to the 60 position to adjust the setting of the speed regulator to bring the plant up to ground idling speed, i whereupon the power lever 3'? is released and is then movable over its range for take-01f and for increase in rotational speed to the maximum rated speed, the latter being, for example, 12,700 E. P. M. with the power lever in its 80 position,

7 operation of the power lever raising the torque and temperature regulator settings and further raising the speed regulator setting. For normal flight, the condition lever is set at 60 and the thrust is varied by operation of the power lever, that is, the turbine is operated at some speed less than the maximum except when maximum power is required and the reduction in speed is made consistent with the best fuel economy for the speed selected.

For combat operation, the condition lever 36 is moved further, for example, to the 73 to 75 position, to control the plant for about the top speed, namely, 12,760 E. P. M., of the turbine. This gives substantially constant or top speed for the range of movement of the power lever, movement of such lever changing the pitch to change thev thrust, in consequence of which the action is quite rapid because the power is thereby increased and applied with very little change in turbine speed and therefore little, if any, acceleration.

For landing, the condition lever is set at the 73 to 75 position and the power lever is moved back toward the 0 position; and, as the plant is operating at the maximum speed fixed by the position of the condition lever, the thrust may be increased very rapidly in the event of waveoff because the rotational speed does not need to be changed to any substantial extent.

With the torque, temperature and speed network components supplied with electrical outputs respectively by the torquemeter, the thermocouple arrangement and the tachometer, such network components operate together as a regulating system or network controlling the power delivered by the turbine to the propeller by regu- I regulating network components, each have settings for raisin and lowering the torque, temperature and speed, as the case may be, at which regulation occurs and the settings are operated by the condition and power levers.

Considering the torque network components, movement of the setting potentiometers raises or lowers the voltage at sliders l 52 and I2ii in consequence of which the potentials at grids 2 and 6 of the tubes, at 553 and'fil, change relatively and the fuel control and pitch control motors are operated to change the fuel flow, and, therefore, the power delivered by the turbine to the propeller; however, movement of the motors moves the sliders to change the grid voltages in the opposite direction and the change m torque, pursuant to fuel change, changes the potential at the grids in such directions as to tend to move each of the motors in a direction opposite to that initiated by movement of the settin Thus, the motors are operated in a follow-up manner to change the power delivered by the turbine to the propeller, the electric circuit being rebalanced with the fuel flow adjusted for zero torque change. In addition to the power setting, the torque network achieves a regulating function minimizing torque deviation for any given setting.

The magnitude of torque is shown by the indicator IIlIa operated by the motor IilI. For zero torque change, the position of slider 9% depends on slider of potentiometer 9d. Assuming an increase in torque, the potential at slider 8c drops, thereby placing the motor Illl in operation to move the slider 98 to a potential point along the resistance having the potential of slider 8d.

In connection with the described control of the potentiometers I I I and I22, it is to be understood that the circuit for potentiometer iii has an altitude setting and that the circuit for the potentiometer I22 has a flight velocity setting so that the fuel flow is influenced by altitude and the propeller pitch by flight velocity. In general, pitch is influenced mainly by velocity and to some extent by altitude, while the contrary is true with respect to fuel.

The temperature network provides a potential which adds algebraically to torque output, the resultant going to the mid-point of the voltage divider, at I38, and being'applied to the grids 2. Thus, increase in temperature, as will increase in torque, tends to decrease the fuel flow and propeller pitch.

The temperature control network includes two controls, one responsive to temperature and a setting, whereby the operating temperature may be Increased as the speed and torque are raised, and the other, an over temperature control, wh1ch comes into play if predetermined temperatures are exceeded in relation to predetermined 7 a switch will be operated to isolate the pitch control motor from the torque, temperature and which potentials are imposed on the grids 2 of tubes, at 50 and 5!, to cause opposite fuel control and pitch control actions, increasing speed being accompanied by decreasing fuel flow and increasing pitch. In addition to this corrective voltage, the speed network also provides a second corrective voltage in the same direction and whose value depends upon means movable in a direction determined by and at a speed depending upon the deviation of the controlling signal from its set value, whereby there i provided compensation to minimize deviation of turbine speed from the setting.

While increasing torque or temperature tends to decrease the fuel input and decrease the pitch, the apparatus correlates temperature and speed so that, While accelerating the engine up to normal operation of Fig. 8, the temperature is maintained as high as practicable and is increased as the rotational speed increases for the development of the power required at any speed without either the temperature or turbine torque exceeding the stall limit for the compressor.

Preferably the main control system is electrical and may assume a wide variety of forms, nevertheless, there is shown, by way of example, main control apparatus, at 32, of theelectronic type constructed and arranged as hereinbefore described and utilizing the torque, speed and temperature inputs to provide outputs for controlling the fuel and the propeller pitch. f

In the event of overspeeding of the plant to a predetermined extent, failure of the main control power supply, a predetermined over-temperature persisting for longer than a predetermined interval, or a predetermined loss of fuel pressure during take-off, there is provided a means responsive to any of these eventualities to shift automatic control of the plant from the main control system to the emergency control system, the pitch motor control being rendered ineffective to vary the pitch of the propeller blades, the by-pass valve of the speed controlled hydraulic arrangement for changing the propeller pitch being closed, and the shift valve an of the fuel control apparatus, at 26, being moved so that fuel entering such apparatus from the feed pump passes through the manual control valve 39 in the fuelair ratio apparatus, at 4|, and then goes through the dump valve and manifold to the atomizers.

To recapitulate briefly the mode of operation, servo-motors control the input of fuel for the turbine and the propeller pitch and each servomotor is controlled by a vacuum tube having a pair of grids to which network Voltages are applied. The network has torque, temperature and speed voltages applied thereto, it has torque, temperature and speed settings, and it has followup or feedback potentiometers operated by the servo-motors. The apparatus regulates for torque, temperature and speed, since deviation in these characteristics, and consequent unbalance of the network, is opposed by the effects of servo-motor operation, such operation continuing until the network is rebalanced. Since the 26. change in torque influences the network immediately, the system is quite rapid in its response and stability i thereby promoted, control being primarily dependent upon torque with, the temperature and speed influences coming in as corrective effects. The settings are controlled by condition and power levers. After starting, normally the condition lever is adjusted to bring the speed up to ground idle speed and thereafter,

speed and power are increased by adjustment of the power lever. For combat or landing, the condition lever is adjusted further to bring the plant approximately up to full speed and the power lever i adjusted over its range to the extent required. With the condition lever in full speed position, a switch is thereby conditioned for switching control of the propeller pitch from the network to the power lever incident to reversal. The system includes a temperature override arrangement whose setting is automatically varied by the attained speed. Further, the main or automatic control system is interrelated to an emergency' one in that, whenever required, changeover from the main to the emergency system is effected automatically.

While the invention has been shown in but one form, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications withoutdeparting from the spirit thereof.

What is claimed is:

1. In aircraft propulsion apparatus, the combination of, a propulsion gas turbine; a variable pitch propeller driven by the turbine by means of a driving connection; means connected with the turbine for supplying fuel for operation of the" turbine; means providing electrical outputs in response to torque of the driving connection between theiturbine and the propeller and in response to turbine speed and temperature; first, second, third and fourth vacuum tube means with said first andsecond vacuum tube means each including a pair of setsof tube elements and each set including a control grid; a normally-balanced controlling electrical network for the grids ofsaid first and second tube means and including a voltage divider having its ends connectedto a first grid of each of the first and second tube means, a speed bridge including said third vacuum tube means forming one of its impedance arms and having its output impressed across the resistance of the voltage divider, a temperature bridge including said fourth vacuum tube means forming one of its impedance arms and having its output impressed on the midpoint of the voltage divider, first and second potentiometers including sliders respectively connected to the second grids of the first and second tube means, means operatively connected withfsaid fourth tube means for varying the impedance of the fourth tube means in response to changes in torque electrical output, means operatively connected with said fourth tube means for varying the impedance of the fourth tube means in response to changes in temperature electrical output, and means operatively connected with said third tube means for varying the impedance of the third tube means in response to changes in speed electrical output; motors operatively con nected with and controlled in response to potential unbalance of the grids of the first and second tube means to vary the fuel input and the propeller pitch and to adjust the sliders of said potentiometers to rebalance the grid potentials; and manually-operable torque, speed and tempera-- 

